[[Image:Phospholipid.gif|right|350px|The structure of a phospholipid]]Phospholipids are [[Lipid|lipid]] molecules which have a [[Phosphate|phosphate]] group attached.

[[Image:Phospholipid.gif|right|350px|The structure of a phospholipid]]Phospholipids are [[Lipid|lipid]] molecules which have a [[Phosphate|phosphate]] group attached.

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They are highly abundant in [[Cell membranes|cell membranes]], where they form a [[Lipid bi-layer|lipid bilayer]], due to the [[Amphiphatic|amphiphatic]] nature of&nbsp;their [[Hydrophilic|hydrophilic]] heads and&nbsp;[[Hydrophobic|hydrophobic]]&nbsp;tails&nbsp;<ref>Alberts et al. (2002) Molecular Biology Of The Cell, 4th edition, New York: Garland Science. p62</ref>.&nbsp;The majority of atoms in the [[Hydrophobic|hydrophobic]] tails are nonpolar and have no&nbsp;charge, this is what makes them insoluble when dissolved in [[Water|water]]. However, the hydrophilic heads are soluble in water due to the presence of either charged groups which are electrostatically attracted to the [[Water|water]] [[Molecule|molecules]],&nbsp;or polar groups which&nbsp;enable [[Hydrogen bonds|hydrogen bonds]] to be&nbsp;form between the heads and the [[Water|water]] [[Molecule|molecules]]&nbsp;<ref>Alberts et al. (2008) Molecular Biology Of The Cell, 5th edition, New York: Garland Science. p620</ref>.<br>

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They are highly abundant in [[Cell membranes|cell membranes]], where they form a [[Lipid bi-layer|lipid bilayer]], due to the [[Amphiphatic|amphiphatic]] nature of&nbsp;their [[Hydrophilic|hydrophilic]] heads and&nbsp;[[Hydrophobic|hydrophobic]]&nbsp;tails&nbsp;<ref>Alberts et al. (2002) Molecular Biology Of The Cell, 4th edition, New York: Garland Science. p62</ref>.&nbsp;The majority of atoms in the [[Hydrophobic|hydrophobic]] tails are nonpolar and have no&nbsp;charge, this is what makes them insoluble when dissolved in [[Water|water]]. However, the hydrophilic heads are soluble in water due to the presence of either charged groups which are electrostatically attracted to the [[Water|water]] [[Molecule|molecules]],&nbsp;or polar groups which&nbsp;enable [[Hydrogen bonds|hydrogen bonds]] to be&nbsp;form between the heads and the [[Water|water]] [[Molecule|molecules]]&nbsp;<ref>Alberts et al. (2008) Molecular Biology Of The Cell, 5th edition, New York: Garland Science. p620</ref>.<br>

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The most common constituent of any [[Lipid bilayer|lipid bilayer]] making up a cell membrane is the phospholipid. Phospholipids are [[Amphiphilic|amphiphilic]]. They have a [[Polar|polar]] head and two hydrocarbon tails, which are [[Non-polar|nonpolar]]. The phosopholipids that make up the&nbsp;cell membranes&nbsp;of plant, bacterial or animal cells often have&nbsp;[[Fatty acids|fatty acids]] tails. Of these two [[Fatty acid|fatty acid]] tails one is unsaturated (contains double bonds) and the other is saturated.&nbsp;This&nbsp;difference causes variation in the length of the tails and thus alters the fluidity of the [[Plasma membrane|membrane]]&nbsp;<ref name="null">Bruce Alberts,Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter, Molecular Biology of the Cell, Fifth edition, 2008, Garland Science, New York. p618</ref>. The chemical make up of the tails can differ. This means that there are many different phospholipids that can make up a cell membrane. The main&nbsp;type&nbsp;found in mammalian cells&nbsp;are [[Phosphoglycerides|phosphoglycerides]] such as [[Phosphatidylcholine|phosphatidylcholine]], [[Phosphatidylserine|phosphatidylserine]] and [[Phosphatidylethanolamine|phosphatidylethanolamine]].&nbsp;These differ in the fact that they have [[Choline|choline]], [[Serine|serine]] and [[Ethanolamine|ethanolamine]] (respectively)&nbsp;attatched to their phosphate groups. phosphatidylserine is the only one that carries a negative chage and all the other [[Phosphoglycerides|phosphoglycerides]]&nbsp;have no charge at physiological pH&nbsp;<ref name="phospholipids">Alberts, Johnson, Lewis, Raff, Roberts, Walter, (2008), Molecular biology of the cell, 5th edition, New York, Garland science, pp620.</ref>.&nbsp;&nbsp;The phospholipid [[Lipid bilayer|bilayer]] acts as a barrier allowing the smaller [[Molecules|molecules]] such as [[Oxygen|O]]<sub>[[Oxygen|2]]</sub>&nbsp; and [[Glycerol|glycerol]] in, but keeping larger molecules such as [[Amino acids|amino acids]] and ions out. The bilayer can be broken down by detergents.<br>

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The most common constituent of any [[Lipid bilayer|lipid bilayer]] making up a cell membrane is the phospholipid. Phospholipids are [[Amphiphilic|amphiphilic]]. They have a [[Polar|polar]] head and two hydrocarbon tails, which are [[Non-polar|nonpolar]]. The phosopholipids that make up the&nbsp;cell membranes&nbsp;of plant, bacterial or animal cells often have&nbsp;[[Fatty acids|fatty acids]] tails. Of these two [[Fatty acid|fatty acid]] tails one is unsaturated (contains double bonds) and the other is saturated.&nbsp;This&nbsp;difference causes variation in the length of the tails and thus alters the fluidity of the [[Plasma membrane|membrane]]&nbsp;<ref name="null">Bruce Alberts,Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter, Molecular Biology of the Cell, Fifth edition, 2008, Garland Science, New York. p618</ref>. For instance, in an unsaturated hydrocarbon tail, the double bonds create kinks so that the molecules do not pack as tightly together, giving rise to a more fluid consistency <ref>Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K and Walter, P. (2008) Molecular Biology of the cell. New York, Garland Science. Pg 59</ref>. Whereas, in a saturated hydrocarbon tail, there are no kinks and thus, the molecules pack together tightly resulting in a less fluid membrane <ref>Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K and Walter, P. (2008) Molecular Biology of the cell. New York, Garland Science. Pg 59</ref>.The chemical make up of the tails can differ. This means that there are many different phospholipids that can make up a cell membrane. The main&nbsp;type&nbsp;found in mammalian cells&nbsp;are [[Phosphoglycerides|phosphoglycerides]] such as [[Phosphatidylcholine|phosphatidylcholine]], [[Phosphatidylserine|phosphatidylserine]] and [[Phosphatidylethanolamine|phosphatidylethanolamine]].&nbsp;These differ in the fact that they have [[Choline|choline]], [[Serine|serine]] and [[Ethanolamine|ethanolamine]] (respectively)&nbsp;attatched to their phosphate groups. phosphatidylserine is the only one that carries a negative chage and all the other [[Phosphoglycerides|phosphoglycerides]]&nbsp;have no charge at physiological pH&nbsp;<ref name="phospholipids">Alberts, Johnson, Lewis, Raff, Roberts, Walter, (2008), Molecular biology of the cell, 5th edition, New York, Garland science, pp620.</ref>.&nbsp;&nbsp;The phospholipid [[Lipid bilayer|bilayer]] acts as a barrier allowing the smaller [[Molecules|molecules]] such as [[Oxygen|O]]<sub>[[Oxygen|2]]</sub>&nbsp; and [[Glycerol|glycerol]] in, but keeping larger molecules such as [[Amino acids|amino acids]] and ions out. The bilayer can be broken down by detergents.<br>

Aside from&nbsp;[[Phosphoglycerides|phosphoglycerides]], another class of lipids commonly found within the body are&nbsp;[[Sphingolipids|sphingolipids]]

Aside from&nbsp;[[Phosphoglycerides|phosphoglycerides]], another class of lipids commonly found within the body are&nbsp;[[Sphingolipids|sphingolipids]]

The most common constituent of any lipid bilayer making up a cell membrane is the phospholipid. Phospholipids are amphiphilic. They have a polar head and two hydrocarbon tails, which are nonpolar. The phosopholipids that make up the cell membranes of plant, bacterial or animal cells often have fatty acids tails. Of these two fatty acid tails one is unsaturated (contains double bonds) and the other is saturated. This difference causes variation in the length of the tails and thus alters the fluidity of the membrane[3]. For instance, in an unsaturated hydrocarbon tail, the double bonds create kinks so that the molecules do not pack as tightly together, giving rise to a more fluid consistency [4]. Whereas, in a saturated hydrocarbon tail, there are no kinks and thus, the molecules pack together tightly resulting in a less fluid membrane [5].The chemical make up of the tails can differ. This means that there are many different phospholipids that can make up a cell membrane. The main type found in mammalian cells are phosphoglycerides such as phosphatidylcholine, phosphatidylserine and phosphatidylethanolamine. These differ in the fact that they have choline, serine and ethanolamine (respectively) attatched to their phosphate groups. phosphatidylserine is the only one that carries a negative chage and all the other phosphoglycerides have no charge at physiological pH [6]. The phospholipid bilayer acts as a barrier allowing the smaller molecules such as O2 and glycerol in, but keeping larger molecules such as amino acids and ions out. The bilayer can be broken down by detergents.